It is required by the manufacturing technique for golf balls that the ball is composed of two hemispheres. The line along which the mold separates is commonly referred to as the equator or the seam line of the ball. Golf balls include a plurality of dimples on the surface to improve the aerodynamics of the ball, but mold manufacturing techniques and ball manufacturing processes require that no dimple intersects with the seam line.
In the past, golf balls were formed with parallel rows, or circles, of dimples, the circles being concentric with the equator. There were three great circles that were not intersected by dimples, one of these being the seam line of the ball. It was found, however, that such a ball is not aerodynamically symmetrical. Later, a ball was formed having no circumferential paths not intersected by dimples except the seam line of the ball. It was necessary, however, to move dimples from the equatorial area, creating asymmetry.
With the imposition of the symmetry rule by the United States Golf Association, the above discussed balls were unacceptable. The symmetry rule requires that the flight of a ball spinning about an axis through the poles be the same as the flight of a ball spinning about an axis through the equator. To conform to the symmetry rule, golf balls have been formed with a plurality of great circles on the ball that are not intersected by dimples, these great circles being known as "false seam lines". Other golf balls have been modified by having the dimples at the poles shallower than the equatorial dimples.
The above discussed techniques for providing aerodynamic symmetry of a ball have the disadvantage that the aerodynamic drag on the ball is increased. Thus, the prior art does not provide a golf ball having aerodynamic symmetry without increase in the coefficient of drag.